This invention relates generally to pressure sensitive mats and in particular to semiconductor pressure sensing mats and circuits for detecting various pressure parameters and performing various functions.
The pressure sensitive treadles or mats of the prior art that were used to activate doors or intrusion detecting devices generally were of the switch type, that is, either the electrical current was switched "on" or "off" when pressure was applied to the mat. Some prior art mats utilized fibrous or porous materials that were impregnated with an electrical conducting material such as graphite or carbon. Such mats were designed to be rather thick and were readily compressible. They operated on the principle that compressing the graphite, carbon or other conductive material, caused a reduction in electrical resistance of the mat core material. In other words, there had to be substantial motion or deflection of the mat material to produce the resistance change. The problem with such mats was their instability under varying conditions of temperature and moisture content. For this reason, accurate measurement of pressures was not possible.